Mercury cathode cell



C. N. RICHARDSON MERCURY CATHODE CELL Filed Nov. 2, 19259 www; 1

Nov. 16, i943.

- INVENTR Ceser ./I/.zcamfan ATTORNEYS Patented Nov. 16,1943

MERCURY CATHODE CELL Chester Northup Richardson, Youngstown, N. Y., asslgnor to The Mathieson Alkali Works, Inc., New York, N. Y., a corporation oi' Virginia.

Application November 2, 1939, serial No. 302,501

(ci. no4-25o) 3 Claims.

This invention is concerned with so-called mercury cells for the electrolysis of aqueous solutions of alkali metal compounds, such,-for example, as sodium chloride, and aims to provide improvements in cell structures with a view to obtaining strength and rigidity, and particularly freedom from buckling of the bottom, while facilitating cell assembly and repair. The invention is concerned particularly with mercury cells having compartments that are several times as long as they are wide, although the invention also affords advantages as applied to cells in which the length does not bear such a great proportion to the width, particularly when the sides of the cells are lined with corrosion-resisting material.

it is customary to carry out electrolytic decomposition oi' solutions of alkali metal compounds, particularly halides, in multiple compartment cells. Thus, an aqueous solution of sodium chloride or brine may be subjected to electrolysis in an anode compartment of an electrolytic cell having a bottom uponwhich a mercury layer rests. The mercury acts as cathode in this compartment and an anode of carbon or the like is disposed in the brine. Passage of current between these two electrodes brings about deposition oi sodium at` the mercury, where it forms an amalgam, and release of chlorine gas which is withdrawn4 from a vapor space overlying the brine. The amalgam is withdrawn from the rst compartment and decomposed in a second or cathode compartment where it comes in contact with an aqueous electrolyte, of say sodium hy-y droxide solution. The amalgam acts as anode in the second compartment and a cathode is disposed in the electrolyte therein overlying the amalgam layer. The sodium released from the amalgam in the second compartment reacts with water to form sodium hydroxide and` hydrogen gas.

For a variety of reasons, it is desirable in large scale operations to make both anode and cathode compartments of a mercury cell relatively long with respect to width and to circulate the brine lengthwise through the anode compartment and the sodium hydroxide or other electrolyte lengthwise through the cathode compartment. Such long compartments should be of very rigid construction for there is a tendency for buckling to occur, and even very slight buckling tends to cause an uneven distribution of mercury overthe bottom of the compartment with consequent impairment of cell efficiency. Moreover, even slight buckling may cause short circuits between the amalgam and the other electrode in the compartment, for example, the anode, because it is customary to leave but little space between the two.

As a. result of my investigations. however, I have i developed an improved cell structure of great My invention contemplates (in an electrolytic cell comprising a compartment, an electrode of amalgam containing an alkali metal disposed upon the bottom of the compartment, an aqueous electrolyte in the compartment overlying an electrode of amalgam, and a second electrode disposed in the electrolyte) the combination which comprises a bottom consisting of a substantially horizontal plate section made of a material that amalgamates but slowly, if at all, with mercury (for example, steel) and having downwardly extending ilange members on its respective sides or longitudinal edges and two side members disposed adjacent the downwardly extending ange members and fastened thereto and extending above the level of the bottom. As indicated hereinbefore, this structure is preferably one in which the bottom is several times as long as it is Wide with the downwardly extending flanges disposed longitudinally.

I have found that this type of structure is much less susceptible to buckling than theretofore customary forms, including compartments formedfrom an up-turned channel, and is capable of advantageous modication depending upon whether it is employed in the construction of an anode compartment or av cathode compartment, and that it offers particular advantages in anode compartments or the like in which it is necessary to provide rubber linings. In an anode compartment, wet chlorine or other corrosive halogen gas usually is formed and such gas Ahas a corrosive action upon steel and many other metals. The steel bottom of the compartment is protected by the overlying mercury layer, but the sides of the compartment should either be constructed of a material which resists attack by wet halogen gas or is covered with a protective lining. Thus, the sides may be formed of porcelain, or more conveniently may be of steel plate to which a lining of rubber or the like is bonded.

I have found that the action of alkali metal amalgam (for example, sodium amalgam) at the interface between a steel plate and a rubber layer bonded thereto tends to destroy the bond,

although it does. not ail'ect substantially thesteel or the rubber themselves. Consequently, it is advantageous to clamp the rubber to the steel near the end oi the plate and also advantageous the ange of the bottom and the side member by bolts or the like. In such a structure, the exposed portion of the bond between the side and the rubber lining is outside the cell and hence free from attack by amalgam. I have also found that it is advantageous to construct the side members with outwardly extending flanges at their top portions. The rubber lining extends upwardly and over the outwardly extending flanges and is clamped at its outer end by a cell cover of concrete or other material resistant to wet chlorine, which rests on top of the rubber and is secured to the outwardly extending flanges by bolts or other clamping means.

In constructing an anode compartment in accordance with my invention, it is convenient to employ as the bottom of the compartment a steel channel having downwardly extending .flanges formed integrally therewith. The downwardly extending anges coupled with the side plates of the compartment give a great rigidity of structure so that the cell or compartment may be made very long with respect to its width without inducing substantial bending or buckling.

In the application of my invention to the construction of a cathodecompartment of a mercury cell, I prefer to employ another modification in which the bottom of the cell is not formed integrally with the ilanges, as in a steel channel, but is composed of a bottom plate reinforced at both edges by metal channels each having a pair of inwardly extending flanges and with their webs disposed substantially vertically. The upper flange of each channel is fastened to the steel plate.

In cathode compartments, the usual electrolyte is sodium hydroxide and neither this nor the evolved hydrogen attack steel or iron substantially. Consequently, it is unnecessary to employ porcelain sides 'or rubber linings and the steel side members may be bolted directly to the downwardly extending flanges of the bottom, in this case the webs of the two channels.

These and other features of my invention will be more readily understood in the light of the lfollowing detailed description of a presently preferred form of mercury cell embodying my invention, taken in conjunction with the accompanying drawing, in which:

Fig. 1 is a cross section through the anode compartment and the cathode compartment of a mercury cell; and Y Fig. 2 is a plan view of the cell of Fig. 1.

l Referring now to the drawing, it will be observed that a mercury cell Ill is provided with an anode compartment II and a cathode compartment I2, which are both several times as long as,

they are wide. Both anode and cathode compartments are disposed substantially horizontally and side by side, but the cathode compartment is slightly higher than the anode compartment. The anode compartment is formed by a bottom member I3 which is an inverted steel channel having its flanges I3A, ISB extending downwardly. I'he sides of the anode compartment comprise a pair of steel angle irons HA, IIB. These are lapped against the flanges of the channel and substantially cover them, and the vertical plate or ange of these angle irons is substantially wider than the horizontal or outwardly extending portion. One flange IBA, IEB of each of the angle irons extends outwardly from the cell at the top thereof; the other portion or web (IBA, ISB) of the angle iron extends down wardly in alignment with the respective flangesy on the steel channel. Rubber linings I 1A, I'lB are cemented or otherwise bonded to the inner faces of the angle irons throughout their length and extend from the bottom of the angle irons around the outer edges of theupper anges thereof. The rubber may be secured to the angle iron by rubber cement or other bonding means. The rubber linings are clampedbetween the flanges of the bottom and the angle irons by means of a plurality of bolts ISA, I8B extending through the webs of the angle iron and the ilanges of the channel.

A mercury layer I9 is disposed on the bottom of the cell, which in this case is formed by the web 20 of the channel. The mercury is overlain by a pool 2I of electrolyte, for example, a sodium lchloride brine, and within the pool there is disposed .an anode 22 of graphite or the like, this being supported by means of a downwardly extending lead-in or bar 23. The top of the anode compartment is closed by means of a cover 23A which may be of any material that is resistant to del composition by wet halogen, for example, concrete which rests on the outwardly extending rubber-covered anges ISA, ISB. The cover is bolted tightly to the flanges. 'I'he lead-in or supporting bar passes through the cover. A vapor space 24 overlying the pool of electrolyte and underneath the cover serves for the accumulation of'chlorine or other halogen gas evolved from the brine and this is' withdrawn through a gas outlet conduit 25 in the cover of the anode compartment adjacent the end thereof.

Current is supplied to the anode compartment from any convenient direct power source (not shown), the power source being connected to the anode through the lead-in and to the mercury amalgam through the steel bottom or inverted channel.

Electrolysis of brine, for example, an aqueous solution of sodium chloride is conducted in the anode compartment in the heretofore customary manner. Chlorine collects at the anode and is withdrawn from the vapor space. Sodiuml collects at the mercury and amalgamates therewith to form an amalgam which is withdrawn and subsequently decomposed in the cathode compartment. Brine to be'decomposed is circulated longitudinally through the anode compartment by miams of a pump (not shown).

ow considering the cathode compartmen the cell, it will be observed that it has a bottolrwiji5 26 formed of a steel plate fastened at its outer edges to a pair of channels 28A, 28B that extend longitudinally of the compartment with their webs 29A. 29B substantially vertical and with their anges 30A, 30B, 3IA, 3IB extending inwardly.

The bottom plate is welded or otherwise fastened y the channels and extend upwardly above the plate but are lapped against the webs of the channels and substantially coverxthem. They are provided at their upper edges with lute members 33A, 33B in which the downwardly extending edges of a cover plate 34 are rested. The lute members are adapted to hold water or other sealing media 35 so as to form a hydraulic seal between the sides of the cathode compartment and the top. A cathode 36 of iron, carbon or the like is disposed in the cathode compartment in a pool 31 of electrolyte, for example, sodium hydroxide. The cathode is underlain by a pool 33 of mercury amalgam which rests upon the bottom plate.

The amalgam ls withdrawn from one end of the anode compartment as it is formed and moved by means of a pump 39 and conduit 40 through a hydraulic seal into the adjacent end of the cathode compartment and ows therethrough longitudinally to the opposite end from which point it is removed and permitted to flow through a conduit 4| and a hydraulic seal back into the anode compartment.

A hydrogen outlet 42 is provided in the top of the cathode compartment adjacent an end thereof. Sodium hydroxide solution formed in the cathode compartment as a result of union between sodium released by the amalgam and hydroxyl radical in the electrolyte is pumped through the cell in a longitudinal direction and circulated through a conventional sodium hydroxide collecting means (not shown) As indicated hereinbefore, the sides of the anode compartment may be formed of porcelain slabs, although these are not so satisfactory as the rubber lined steel angles, illustrated in Fig.A l.

I claim:

1. In an electrolytic cell comprising a compartment, an electrode of mercury amalgam containing an alkaline metal disposedupon the bottom of the compartment, an aqueous electrolyte in the compartment overlying the electrode of mercury amalgam and a second electrode disposed in the electrolyte, the combination which comprises a steel bottom consisting of a plate section and a pair of ange members on the underside of the plate and extending downwardly at its respective edges, said downwardly extending flanges being formed of metal channels having their flanges turned inwardly with their webs in an upright position, and a pair of side members disposed adjacent the respective flanges and fastenedthereto and substantially covering the webs of the channels and extending above the level ofthe bottom plate section, the flange members being entirely below the bottom plate, with the latter extending substantially from side member to 'side member.

2. In an electrolytic cell comprising a compartment, an electrode of mercury amalgam containing an alkaline metal disposed upon the bottom of the compartment. an aqueous electrolyte in the compartment overlying the electrode of mercury amalgam and a second electrode disposed in the electrolyte, the combination which comprises a compartment having a bottom formed of a steel channel with its web disposed substantially horizontally and with its flanges extending downwardly entirely below the web, two side members disposed over the respective ilanges and fastened thereto but extending upwardly above the web of the channel, and rubber linings disposed within the compartment covering the two sides and bonded thereto and clamped between the ilanges of the channel and the side members.

3. In an electrolytic cell comprising a compartment, an electrode of mercury amalgam containing an alkaline metal disposed upon the bottom of the compartment, an aqueous electrolyte in the compartment, overlying the electrode of mercury amalgam and a second electrode disposed in the electrolyte, the combination which comprises a compartment having a bottom formed of a steel channel with its web disposed approximately horizontally and with its fianges extending downwardly entirely below the web, two side members lapped over the respective flanges longitudinally of the compartment and fastened to the flanges but extending upwardly above the web of the channel, a pair of top flanges extending outwardly from the upper edges of the respective side members, a top member disposed above the anges of the side members, and rubber linings disposed adjacent the side members and bonded thereto and within the compartment, said rubber linings extending respectively over the top flanges and between the sides of the flanges of the channel. the linings being clamped between the flanges of the channel and the respective side members and between the flanges on the side members and the top member.

l CHESTER NORTHUP RICHARDSON. 

